Cesarean delivery rates in the US and Canada are substantially higher than in most other developed countries with comparable or lower rates of perinatal mortality and morbidity. Objective 14.8 of "Healthy People 2000" is to reduce the US cesarean rate to 15% by the year 2000, from a baseline of 24.4% in 1987. In the Mid-course Review, only about 20% of the target decrease had been achieved. "Labor support" is the term used to describe a repertoire of techniques to help women during labor, through offering companionship, attention to their emotional needs, and comfort measures. Despite persuasive evidence that the amount of support women receive from caregivers during labor will influence cesarean delivery rates and other adverse childbirth outcomes, studies show that nurses spend relatively little time in providing support. The primary aim of this large, multi-center randomized control trial is to rigorously evaluate the effectiveness of nurses as providers of support for laboring women. A secondary aim is to compare the costs of a policy of continuous nursing support versus a policy of usual, intermittent nursing care. After overcoming two major barriers to the effective provision of labor support by nurses (inadequate training and inflexible staffing models), the trial will enroll 6900 women at hospitals in the US and Canada. Laboring women who consent to participate will be randomly allocated to either continuous nursing support or usual, intermittent nursing care. While the primary outcome of interest is the cesarean delivery rate, the trial will also evaluate the effectiveness of labor support in reducing a variety of other short- and long-term physical and psychosocial problems for mothers and their infants. The results will enable informed policy decisions about staffing hospital delivery suites and make a substantive contribution to knowledge concerning the effectiveness of labor support in reducing a number of adverse childbirth outcomes, including prolonged hospital stay, postpartum depression, and early cessation of breastfeeding.